The club, run by chief executive Ed Woodward, spent just over £10m on 'registered intermediaries' in the period between October 1 2015 and February 1 2016 - £3.35m more than Liverpool, who spent the second most at £6.67m.
United, who are currently two points outside the Champions League places, spent almost twice as much as neighbours Man City, who spent the third-most at £5.88m.
In that time the club, managed by Louis van Gaal, have not signed a single player nor renewed any contracts, while they sold Ben Pearson and Liam Grimshaw to Preston and loaned out six players including James Wilson and Victor Valdes.
Arsenal were fourth on the list, having spent £3.135m, but only bought Mohamed Elneny from FC Basel in January, while loaning out three players including Mathieu Debuchy and Yaya Sanogo.
West Ham, also chasing a place in the top-four, spent £2.691m, marginally more than London rivals Tottenham (£2.562m), who are pushing Leicester for the Premier League title.
Current league-leaders the Foxes paid just £936,000 - the fourth lowest in the top flight.
Full list of intermediary and agents' fees:
Manchester United £10,023,318
Manchester City £5,880,098
West Ham United £2,691,331
Stoke City £1,748,093
West Bromwich Albion £1,700,127
Aston Villa £1,638,571
Crystal Palace £1,197,845